1. Field of the Invention
The present invention generally relates to an end effector for transporting a workpiece such a semiconductor wafer between a transferring chamber and a processing chamber for processing a workpiece, for example.
2. Description of the Related Art
A process of semiconductor manufacturing includes a step of transporting a semiconductor wafer from a wafer-storing cassette to a processing chamber via a transferring chamber using a robotic arm or a step of transporting a semiconductor wafer from a processing chamber to another processing chamber using a robotic arm. The robotic arm is provided with an end effector for loading a wafer thereon and carrying the wafer from one chamber to another. Typically, the end effector does not have a mechanical clamping mechanism for clamping a wafer, and by a wafer positioning or alignment mechanism (e.g., those disclosed in U.S. Patent Application Publication No. 2012/0325148, U.S. Pat. No. 7,963,736, and U.S. Pat. No. 8,041,450, each disclosure of which is herein incorporated by reference in its entirety), a wafer is placed on the end effector for transfer. The wafer stays on the end effector while being carried by friction against a surface of the end effector, which is caused by gravity. As throughput is increased, the transferring speed by the robotic arm is also increased. When the transferring speed is increased, since the wafer stays on the end effector by friction, the wafer sometimes moves relative to the end effector and slips out of place, thereby causing a transfer error and decreasing transfer stability.
Further, when a wafer is transferred in a vacuum atmosphere in order to suppress generation of particles, use of a mechanical clamp or an end effector having sloped periphery protrusions for receiving the periphery of a wafer thereon is difficult. That is, with use of a mechanical clamp, when the mechanical clamp contacts a wafer, the mechanical clamp may damage a film near the edge of the wafer, generating particles. Also, with use of the end effector having sloped periphery protrusions, when a wafer slips downward along the sloped periphery protrusions for positioning the wafer, the edge of the wafer rubs against the sloped periphery protrusions, generating particles. Further, an electrostatic chuck has problems in requiring charging and discharging time, and adsorbing particles. Thus, placing a semiconductor wafer on support pins of an end effector and carrying the wafer slowly may be preferable as a method for transporting a semiconductor wafer. However, as mentioned above, the method has a demerit that transportation speed cannot be increased.
At least one embodiment of the present invention can effectively resolve at least one of the above problems. It should be noted that any discussion of problems and solutions involved in the related art has been included in this disclosure solely for the purposes of providing a context for the present invention, and should not be taken as an admission that any or all of the discussion were known at the time the invention was made.